grainNoun A very small unit of weight, in England equal to 1/480 of an ounce troy, 0.0648 grams or, to be more exact, 64.79891 milligrams. A carat grain or pearl grain is 1/4 carat or 50 milligrams. The old French grain was 1/9216 livre or 53.11 milligrams, and in the "mesures usuelles" permitted from 1812 to 1839, with the livre redefined as 500 grams, it was 54.25 milligrams.

grainNoun ("materials") A region within a material having a single crystal structure or direction.

grainVerb To feed grain to.

grainVerb To make granular; to form into grains.

grainVerb To texture a surface in imitation of the grain of a substance such as wood.